The invention relates generally to the field of inkjet printing, and more specifically to methods of coating inkjet recording substrates.
Porous inkjet recording media are often coated with inorganic oxide particles to improve the rate of ink absorption. Such particles also improve the quality of images printed on the media, improving such properties as color gamut, gloss, coalescence, and bronzing.
Inorganic mineral oxide particles can be bound to an inkjet substrate, and to themselves, using a variety of known polymeric binders, the most common of which are polyvinyl alcohols (PVAs). Many PVAs are water-soluble and exhibit good binding both to inorganic oxide particles and to natural (e.g., cellulosic) and artificial (e.g., extruded polyethylene photo paper) substrates. Typically, inorganic oxide particles are suspended in a mixture of PVA and water and the suspension is applied to an inkjet printing substrate (e.g., paper), which is then dried and cut to yield finished inkjet printing sheets. Such a sheet is commonly referred to as a porous inkjet receiver, and ink applied to its surface appears to dry nearly instantly.
Mineral oxide-coated inkjet printing sheets exhibit several significant drawbacks. Separation of coating from the sheet (e.g., upon abrading or bending the sheet) and cracking within the coating leads to poor initial quality of the sheet and/or degradation over time of an image printed thereon. In order to minimize this problem, the coating can be dried slowly during manufacture, increasing the manufacturing cost. This problem can be improved by increasing binder level, but print qualities such as coalescence and ink absorption rate can be deteriorated by including additional binder. A need exists for inkjet printing substrates that do not exhibit these drawbacks.
One method of alleviating these drawbacks that has been proposed (e.g., U.S. Patent Application Publication No. 2002/0081419 and U.S. Patent Application Publication No. 2004/0014857) is using silanol-modified polymers to both cross-like the mineral oxide particles and to bind them to the substrate. Drawbacks of this approach include the high cost of silanol-modified polymers, premature crosslinking, and gelation of the coating fluids in the presence of the silanol-modified polymers. The present invention overcomes drawbacks in the prior art.